The Chiral Quark-Soliton model of the nucleon contains a mechanism for an attractive interaction between nucleons. This, along with the exchange of vector mesons between nucleons, is used to compute the saturation properties of infinite nuclear matter. This provides a new way to asses the effects of the nuclear medium on a nucleon that includes valence and sea quarks. We show that the model simultaneously describes the nuclear EMC effect and the related Drell-Yan experiments.One frontier of strong interaction physics lies in the intermediate range of length scales available to present experiments where neither the fundamental theory, Quantum Chromodynamics (QCD), nor its low energy effective theory, Chiral Perturbation Theory, have useful perturbative expansions. Neither fundamental quarks nor point-like hadrons provide a complete description, so including the non-perturbative information that hadrons are bound states of valence quarks in a polarized vacuum is necessary. One way to probe these intermediate length scales and this non-perturbative physics is to examine the short distance structure of a large object. The prime example is the European Muon Collaboration (EMC) effect [1] where the short distance (∼ 5 GeV, or ∼ 10 −2 fm) structure of nuclei differs from that of a collection of free nucleons. This measurement showed that bound nucleons are different than free ones, and implied that the medium modifications could be significant for any nuclear observable [2]. Indeed, a recent paper [3] obtains evidence for a medium modification of the elastic proton form factor.Our central concern is the depletion of the nuclear structure function F A 2 (x) in the valence quark regime 0.3 < ∼ x < ∼ 0.8. While the general interpretation is that a valence quark in a bound nucleon has less momentum than in a free one, corresponding to some increased length scale, the specific mechanism for this has eluded a universally accepted explanation for 20 years [2,4,5,6]. A popular explanation is the so-called 'binding' effect which originates from a possible mechanism in which mesons binding the nucleus carry momentum. An important consequence is that the mesonic presence would enhance the anti-quark content of the nucleus [7,8]. Such an effect has not been seen in Drell-Yan experiments [9] in which a quark in a proton beam annihilates with an antiquark in a nuclear target producing a muon pair. Furthermore, relativistic treatments, including the lightcone approach needed to obtain the nucleon structure function, of the binding effect with structureless hadrons fail [10,11,12,13], suggesting that modifications of the internal quark structure of the nucleon are required to explain the deep inelastic scattering data.Any description of the EMC effect must be consistent with the constraints set by both deep inelastic scattering and Drell-Yan data. Thus a successful model must include antiquarks as well as quarks, and show how the medium modifies both the valence and sea quark distributions. Our purpose is to provide a mechanis...
We calculate the electromagnetic form factors of a bound proton. The Chiral Quark-Soliton model provides the quark and antiquark substructure of the proton, which is embedded in nuclear matter. This procedure yields significant modifications of the form factors in the nuclear environment. The sea quarks are almost completely unaffected, and serve to mitigate the valence quark effect. In particular, the ratio of the isoscalar electric to the isovector magnetic form factor decreases by 20% at Q^2=1 GeV^2 at nuclear density, and we do not see a strong enhancement of the magnetic moment.Comment: 13 pages, 6 figures, Added references and a clearer connection to experimen
The relationship between the properties of nuclear matter and structure functions measured in lepton-nucleus deep inelastic scattering is investigated using light front dynamics. We find that relativistic mean field models such as the Walecka, Zimanyi-Moszkowski (and point-coupling versions of the same) and Rusnak-Furnstahl models contain essentially no binding effect, in accord with an earlier calculation by Birse. These models are found to obey the Hugenholtz-van Hove theorem, which is applicable if nucleons are the only degrees of freedom. Any model in which the entire Fock space wave function can be represented in terms of free nucleons must obey this theorem, which implies that all of the plus momentum is carried by nucleons, and therefore that there will be essentially no binding effect. The explicit presence of nuclear mesons allows one to obtain a modified form of the Hugenholtz-van Hove theorem, which is equivalent to the often-used momentum sum rule. These results argue in favor of a conclusion that the depletion of the deep inelastic structure function observed in the valence quark regime is due to some interesting effect involving dynamics beyond the conventional nucleon-meson treatment of nuclear physics.miller/jasons/reorder.tex
A light front formalism for deep inelastic lepton scattering from finite nuclei is developed. In particular, the nucleon plus momentum distribution and a finite system analog of the Hugenholtzvan Hove theorem are presented. Using a relativistic mean field model, numerical results for the plus momentum distribution and ratio of bound to free nucleon structure functions for Oxygen, Calcium and Lead are given. We show that we can incorporate light front physics with excellent accuracy while using easily computed equal time wavefunctions. Assuming nucleon structure is not modified in-medium we find that the calculations are not consistent with the binding effect apparent in the data not only in the magnitude of the effect, but in the dependence on the number of nucleons.
The relationship between the properties of nuclear matter and structure functions measured in lepton-nucleus deep inelastic scattering is investigated using light front dynamics. We find that relativistic mean field models such as the Walecka, Zimanyi-Moszkowski (and point-coupling versions of the same) and Rusnak-Furnstahl models contain essentially no binding effect, in accord with an earlier calculation by Birse. These models are found to obey the Hugenholtz-van Hove theorem, which is applicable if nucleons are the only degrees of freedom. Any model in which the entire Fock space wave function can be represented in terms of free nucleons must obey this theorem, which implies that all of the plus momentum is carried by nucleons, and therefore that there will be essentially no binding effect. The explicit presence of nuclear mesons allows one to obtain a modified form of the Hugenholtz-van Hove theorem, which is equivalent to the often-used momentum sum rule. These results argue in favor of a conclusion that the depletion of the deep inelastic structure function observed in the valence quark regime is due to some interesting effect involving dynamics beyond the conventional nucleon-meson treatment of nuclear physics. miller/jasons/reorder.tex
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